This invention relates generally to shearing systems. It relates more particularly to apparatus and a method for clamping and shearing sheet material and, specifically, to a method for shearing sheet steel to prepare it for laser welding.
In general, shearing systems consist of a shear assembly having an upper and lower frame, and a slide plate. A die assembly with upper and lower shoes is positioned within the shear assembly. Each of the shoes includes a clamp arrangement and blade arrangement. Sheet material such as sheet metal to be cut is placed in a gap between the upper and lower shoes and is positioned with guide apparatus. Hydraulic cylinders are used to drive the slide downward against the upper shoe, depressing it. As the upper shoe is depressed in a downward stroke, first an upper clamp contacts the sheet metal and presses it against a lower clamp. As the upper shoe continues its downward stroke, the sheet is sheared by an upper blade sliding past lower blades.
One problem with conventional shearing systems is that often the sheet is clamped with a bend or a wave in it. This causes the sheet to be sheared while it is not perfectly flat. Accordingly, when the sheet springs back to its pre-clamped state, the sheet has a cut-edge which is not as straight as was intended.
Another problem with conventional shearing systems is that sheet metal may be only partially sheared. In other words, the cut-edge of the sheet may have a rough and pitted area resulting from splitting or breaking rather than from the shearing action of the blades. The rough and pitted area may be difficult to weld to another sheet.
Another problem with conventional shearing systems is that the guide for upward movement of the upper shoe works against the guide for downward movement of the upper shoe. Accordingly, the guides incur increased wear.
It would be desirable to have a shearing system that would clamp the sheet without trapping waves or bends so that a straight cut would be achieved. It would also be desirable to have a blade arrangement that would maximize the actual shearing of the metal sheet with minimal breakage of the cut-edge. It would also be desirable to have a die assembly guide arrangement which would provide a smooth transition between the open and closed position of the die assembly and reduce wear on the guides.
The invention includes apparatus for clamping sheet material to be sheared including a die shoe, and a plurality of spring clamping members positioned longitudinally along the die shoe. The clamping members are positioned in raised, stepped sequence outwardly from the centerline of the shoe, perpendicular to the longitudinal sides of the shoe, whereby they sequentially contact the sheet. Each of the clamping members may include a guide pin positioned between two mechanical springs.
The clamping apparatus may further include a second shoe with a clamp opposing the clamping members on the first die shoe to securely hold a sheet during the shearing operation. The first and second die shoes are preferably upper and lower die shoes, respectively. The clamp and the clamping members preferably each include a sandblasted and chromed, sheet contact surface. The second die shoe may include an opening formed therein for allowing the scrap cut from the sheet to fall onto a conveyer traveling in a direction parallel to the longitudinal side of the second die shoe.
The invention further includes a method of clamping sheet material to be sheared. A die assembly, including first and second die shoes with opposing clamps, is provided. The first die shoe clamp comprises a plurality of clamping members. The sheet material is contacted with these clamping members positioned on opposite sides of, and adjacent to, a centerline, perpendicular to the longitudinal sides of the die assembly. The sheet material is sequentially contacted with the clamping members beginning at the centerline and proceeding outwardly from the centerline, to secure the sheet between the first and second clamps prior to shearing.
The invention further includes apparatus for shearing sheet material which includes the die assembly with the first and second die shoes. In the apparatus the first die shoe is adapted to slidably fit in a shear assembly. Linear bearings are positioned in the shear assembly adjacent the corners of the die assembly. A guide rail is slidably fitted in each of the linear bearings to guide the movement of the first die shoe toward the second die shoe. Gas springs are positioned adjacent each of the linear bearings, which gas springs are adapted to compress during the movement of the first die shoe toward the second die shoe and then expand to force the first die shoe back to an open position, all without working against the shear guide posts. Preferably, the linear bearings extend beyond a cut line. This arrangement adds rigidity and stability to the die assembly. The linear bearings each preferably comprises a U-shaped channel member, which contains ball bearings, to allow the guide rail to move vertically within the linear bearing.
The invention further includes a method of shearing sheet material. According to the method, a first or upper die shoe of the die assembly is guided downwardly along the linear bearings, while simultaneously compressing the gas springs. The gas springs then expand to reposition the upper die shoe of the die assembly.
The invention further includes apparatus for shearing sheet material which includes a cutting blade adapted to be attached to a die shoe. The blade is positioned at an angle to the horizontal. This results in the cut-edge of the sheet having a higher percentage of sheared surface area and a lower percentage of broken surface area. Preferably, the cutting blade is positioned at an angle of between about 0.2 and 0.5 of a degree from the horizontal. The apparatus may further include a second cutting blade, adapted to be attached to a second shoe which blade has a rake design. The second blade preferably has a rake of approximately {fraction (3/16)} inch per foot.
The invention further includes apparatus for shearing sheet material wherein the shear assembly includes an upper frame and a lower frame, bolted together. The upper frame includes a hydraulically operated slide plate. The die assembly includes an upper shoe and lower shoe. The upper shoe includes an upper clamp and an upper blade. The lower shoe includes a lower clamp plate and a lower blade.
The upper clamp includes a plurality of spring-loaded clamping members which press downwardly upon the sheet material, sequentially outwardly from adjacent and center line extending perpendicular to a longitudinal side of the die assembly. These clamping members secure the sheet material to the lower clamp when the upper shoe and upper clamp are pressed downwardly by the slide plate.
The lower frame may include hydraulically controlled locating pins which are received in openings formed in a bottom portion of the lower shoe. The die assembly may also include a plurality of linear bearings with guide rails for guiding the upper shoe when it is driven downward by the slide plate. The die assembly may also include a plurality of gas springs which compress while the upper shoe is driven downward by the slide plate, and expand after the slide plate is retracted to force the upper shoe upwardly to an open position. The spring-loaded clamping members may include at least one mechanical spring and a guide pin. The invention may further include a torque tube which is oriented longitudinally in said shear assembly and is connected to a cam which pivots vertically and is trapped between the slide plate and a bearing housing. The torque tube maintains the slide plate in parallel relationship with the lower frame.
The apparatus of the invention may further include a scrap conveyer assembly. The scrap conveyer assembly is positioned within the shear assembly, perpendicular to the direction of sheet insertion into the die assembly.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
The invention, together with further objects and attendant advantages, will best be understood by reference to the following detailed description of the presently preferred embodiment of the invention, read in conjunction with the accompanying drawings.